1. Field of Invention
The present invention relates to a clasp for securing a coupled member such as a strap or a band. The invention also relates to a band that has this clasp, to a portable device that has the band, to a timepiece, and to an accessory.
2. Description of Related Art
One type of conventional clasp for securing the free ends of a timepiece band has a frame disposed freely pivotably to the band with a protruding stud, and a push button catch that holds the stud with spring force. See, for example, Japanese Unexamined Patent Appl. Pub. JP-A-H10-28605.
The stud part of this clasp has a small diameter shank that rises from the frame, and a larger diameter head at the distal end of the shank. When the clasp is closed and locked, the stud is inserted through a hole in the band and the large diameter head of the stud protruding from the hole in the band is engaged and held in the hole in the push button catch.
Some problems with the clasp taught in Japanese Unexamined Patent Appl. Pub. JP-A-H10-28605 are described below.
(1) Every time the band is attached to and removed from the wrist, the stud must pass through a hole in the band. Every time the stud is removed from a hole in the band, the large diameter head of the stud catches the edge of the engaged hole in the band on the back side of the band, and the area around the hole is thus easily damaged. More specifically, when the timepiece is held by the band on the wrist, the rigidity of the band produces tensile force that causes the shank of the stud to be offset from the center of the hole in the band so that the small diameter part of the stud contacts the inside circumference surface of the hole. When the stud is then removed from the hole, the large diameter head catches the edge of the hole in the band, and the area around the hole is thus easily damaged.
As a result, when the clasp causes the push button catch to engage a stud at a hole in the band, a load acts on only a part of the band when the clasp is opened and closed, and the durability of the band is thus low.
(2) Aligning the stud with the hole in the band when inserting the stud into the hole can be difficult, and securing the clasp can therefore be difficult. More particularly, the two parts of the band must be correctly positioned together when connecting the two free ends of the band, and the stud attached to the end of the one band must be positioned to the hole in the other band, but the stud is hidden on the back side of the band and is difficult to see.
Even if the stud is disposed to a position on the opposite side described in Japanese Unexamined Patent Appl. Pub. JP-A-H10-28605, such as when the stud is disposed to a plate member that contacts the wrist and the opposing band is placed over the plate to pass the stud through the hole, the stud is still hidden on the back side of the band. This means that it is still difficult to align the stud with the hole in the band, and it is still difficult to secure the band.
Furthermore, if there are multiple holes in the band there is no assurance that the stud will always pass through the desired hole when putting the band on, and the length of the fastened band may therefore differ from the desired length.